When naive T cells encounter foreign antigen along with proper co-stimulation and cytokines, they undergo rapid and extensive clonal expansion and differentiate into specific lineages. Two closely related lineages in CD4+ T cells are TH17 cells, which promote inflammation, and Treg, which dampen immune responses. Recent work from us and others has shown that T cell metabolic pathways are tightly and ubiquitously linked with T cell differentiation and immune functions, implicating a great potential for modulating T cell immune responses through targeting metabolic processes. Recent work from us and others indicated a preference on glycolysis during TH17 differentiation but not during iTreg differentiation, and suggests that such metabolic preferences play a role in driving cell fate towards TH17 or iTreg. These studies indicate the presence of T cell lineage- specific metabolic programs and cell intrinsic mechanisms of metabolic regulation of T cell differentiation. However, the complete profile of T cell lineage-specific metabolic programs, the regulatory mechanisms of metabolic reprogramming during T cell differentiation and the potential therapeutic application of targeting T cell metabolic programs remain elusive. Our studies to date have implicated the transcription factor Myc as one of the key nodes coordinately regulating TH17 cell metabolism and differentiation. We therefore hypothesize that the Myc-mediated metabolic reprogramming and metabolic checkpoint fuels TH17 differentiation and represents a novel therapeutic target of autoimmune diseases. Our goals follow directly from this hypothesis and we propose to apply biochemical, cellular and genetic approaches to investigate the role of Myc and metabolic reprogramming in regulating T cell differentiation. Specifically, we will: a) determine the TH17 lineage-specific metabolic reprogramming, metabolic addiction and the role of Myc in regulating TH17 metabolism and differentiation (aim 1); b) elucidate the dynamic interplay among Myc, TORC1 and HIF1? in mediating a metabolic checkpoint in TH17 differentiation (aim 2); and c) assess the metabolic program as a novel therapeutic target for TH17-mediated autoimmune diseases (aim 3). Our proposal employs genetic models and metabolic approaches and focuses on TH17 cells as a starting point to dissect how the metabolic pathway regulation impacts immune responses in physio-pathological settings. The insights generated from this study will reveal fundamental interplays between signaling pathways and metabolic pathways in the immune system. These studies of immune metabolism may identify novel therapeutic intervention strategies for inflammatory and autoimmune diseases.